1. Technical Field
The present invention relates to polymer composite materials and more particularly to polymer composite materials used as abrasives and more particularly as a blast media. Still more particularly, this invention relates to the use of nano-structure composite materials as an abrasive and a blast media.
2. Background Information
Various methods and compositions are taught in the prior art for the stripping of organic coatings from an underlying metal or composite substrate by means of polymer abrasives. Such polymer abrasives have the advantage of being harder than the organic substrate but softer than the underlying substrate.
U.S. Pat. No. 4,731,125, for example, discloses a process whereby paint is removed from composites by blasting with urea-formaldehyde plastic particles having a Mohs scale hardness of 2.5-3.5 with a flow at a pressure of 40 lb/in2.
U.S. Pat. No. 4,947,591 discloses a process whereby paint is removed by impact with particles of an acrylic-containing unsaturated polyester where the particles are ground from a cured mass so as to have at least 40 facets per particle.
U.S. Pat. No. 5,112,406 discloses a process for removing coatings from sensitive hard surface metal composite surfaces, masonry, stucco, plaster or wood by blasting the surfaces with a high velocity fluid stream containing water soluble crystalline sodium sulfate particles admixed with a hydrophobic silica or hydrophobic polysiloxane flow/anti-caking agent.
U.S. Pat. No. 5,160,547 discloses a process where the surfaces are blasted with water saturated compressed air stream under pressures of 10-150 psi using sodium bicarbonate particles having particle sized of 250-300 microns in admixture with a hydrophobic silica flow/anti-caking agent.
U.S. Pat. No. 5,147,466 discloses fine particles or oil films which are cleaned from the surface by bombarding it with fine frozen particles of water or other liquids such as glycerin carried in a stream of nitrogen cooled air under relatively low pressure.
U.S. Pat. No. 5,221,296 discloses abrasives based on finely divided abrasive particles bonded to one another and/or to a support by means of a binder, where the binder is the solid component of an aqueous polymer dispersion which is obtainable by polymerizing unsaturated monomers which can be polymerized by means of free radicals in the aqueous phase of a monosaccharide, oligosaccharide, polysaccharide, oxidatively, hydrolytically and/or enzymatically degraded polysaccharide, chemically modified monosaccharide, oligosaccharide or polysaccharide or a mixture of the above.
U.S. Pat. No. 5,308,404 discloses a process by which contaminants are removed from substrates by blast cleaning with a media containing abrasive particles obtained by compacting fine particles of the abrasive into larger particles having a hardness of 2-5 Mohs and wherein the abrasive can be water (soluble or insoluble) and is preferably sodium bicarbonate or calcium carbonate.
U.S. Pat. No. 5,316,587 discloses blast cleaning a solid surface which includes the steps of propelling an abrasive blast medium against a solid surface using a water-containing pressurized fluid stream to strip contaminants from the surface wherein the blast medium comprises water soluble abrasive particles and a surfactant.
U.S. Pat. No. 5,322,532 discloses a process for removing contaminants from a substrate comprising blast cleaning the substrate with composite abrasive particles formed by agglomerating particles of sodium bicarbonate with a aqueous binder solution of sodium carbonate.
U.S. Pat. No. 5,360,903 and U.S. Pat. No. 5,367,068 disclose a process whereby a surface is treated with particles of a glassy polysaccharide wherein the apparent hardness of the granules is between that of the coating and of the substrate and the granules are of starch, preferably wheat starch with dextrose equivalent less than 10, preferably unhydrolyzed.
U.S. Pat. No. 5,380,347 discloses a blast media for stripping contaminants from a solid surface comprising abrasive particles and a surfactant in the form of a granular surfactant-clathrate compound formed of a surfactant and a water soluble compound having clathration capability such as urea. The surfactant reduces the amount of water-soluble residues, which remain on the targeted surface and enhances the removal of dirt, grease and oil from the targeted surface.
U.S. Pat. No. 5,427,710 discloses a composition useful for removing polymeric coatings from flexible and inflexible surfaces which consists essentially of a conjugated terpene, an alcohol, a non-conjugated terpene, a surfactant and an organo-clay rheological additive.
U.S. Pat. No. 5,780,619 discloses a starch graft poly(meth)acrylate blast media which is effective in paint removal. The media is superior to a physical blend of the components (i.e., starch and acrylic polymers) and to wither a starch polymer or an acrylic polymer used singly. The hardness of the media is between 65-90 Shore D.
A need, however, exists for ways to improve the speed and effectiveness of such stripping procedures. A need also exists for ways of decreasing the breakdown rate of abrasives used for this purpose.
It is an object of the present invention to provide a polymeric blast media which efficiently and cost effectively removes organic coatings from substrates.
It is a further object of the present invention to provide a polymeric blast media which allows rapid removal of organic coatings from substrates.
It is a further object of the present invention to provide a polymeric blast media which can be used to remove standard organic coatings without substantial risk of damage to sensitive metal or composite substrates.
It is a further object of the present invention to provide a polymeric blast media which has a high degree of durability.
It is a still further object of the present invention to provide a polymeric blast media which has favorable surface roughness, almen arc, and water absorbence characteristics.
These and other objects are met by the present invention which is a method for making a polymeric blast media, and a product of this method. The first step involves blending a melamine compound with a cellulosic material and compression molding said first blend to produce a compression molded first blend. This first blend is then cooled and then ground. In the next step of this method, a urea compound is blended with a nano-clay material to produce a second blend and compression molded. This compression molded second blend is then ground to produce a particulate second blend. The particulate first blend is then blended with the particulate second blend.
In another preferred embodiment, a cross linked cast acrylic is ground to a particulate material and blended with the first and second blends.
In another preferred embodiment, the particles in the blast media are coated with a polyurethane coating.
In another preferred embodiment, a glass oxide or metal oxide dense particulate material is incorporated with the blast media.
The present invention also encompasses an abrasive media for the removal of coating or for the preparation of surfaces prior to coating or cleaning comprising a thermosetting polymer with an additive, wherein the additive has a major dimension and a minor dimension and said minor dimension is from about 1nm to about 20 nm. The additive may be the nano-clay material, or alternatively may be a polyhedral oligomeric silsesquioxane material.
The present invention also encompasses a method of making a sanding pad for removing an organic coating from a substrate comprising the steps of blending a liquid polymeric material with a nano-clay material to produce a first blend, blending a cellulosic material with said first blend to produce a second blend. This second blend is then extruded to form a continuous sheet of abrasive material into a plurality of individual pads.
The blast media of this invention may be used for removal of standard aerospace coatings such as epoxy primers and polyurethane topcoats from very sensitive metal or composite substrates with better efficiency than was previously available. This media coating can be removed at accelerated speeds as compared to prior art blast media. The safety factor of this media on thin skin aluminum or composite surfaces is high. Coatings can be removed with virtually no damage to such substrates, leaving protective coatings such as cladding and anodizing intact. Also, the durability of this media helps to maintain economic feasibility in large-scale aerospace applications. Various different embodiments of this media address specific applications related to the aerospace industry and industry in general. All of these embodiments make use of nanometer-sized montmorillonite clay particles, which improve surface integrity and provide advantages in the mechanical and thermal properties of the polymer. These results are achieved with no increase in specific gravity due to the very low amounts of nano-particle needed, i.e. between xc2xd% and 5% by weight. These results demonstrate that the overall increase in efficiency of this media is three to four times faster than unfilled polymer while the durability has more than doubled.